Substance abuse among persons with severe mental illness (SMI) has caused increasing concern over the past decade. Co-occurring substance abuse exacerbates symptoms, confuses diagnosis, and complicates illness, contributing to costly repeated admissions to acute psychiatric care. The growing literature on this problem does not identify a treatment of choice. Nevertheless, it supports integration of substance abuse treatments with comprehensive and clinically sophisticated programs for SMI individuals. Intensive case management models show promise as a means of achieving this integration, but controlled research has been limited. The aim of this randomized clinical trial is to compare an intensive case management model to another comprehensive service delivery model for frequently hospitalized SMI with co-occurring substance abuse disorders. The intensive case management model, Clinical Case Management (CCM), integrates assertive brokerage with outpatient therapy offering total, ongoing support through a single provider. Clinical Case Management will be compared to an Expanded Brokerage Team (EBT) that is available during critical periods following hospitalizations. EBT members provide no direct treatment, but assertively link clients to community services. We will examine clinical efficacy and cost of these models simultaneously In an integrated design. A total of 400 individuals, stratified by presence versus absence of substance use disorders, will be randomly assigned from within strata to CCM or to EBT and followed for 18 months. The interventions will be monitored to provide precise data about treatment fidelity. The main hypothesis to be tested is that there will be an interaction of the interventions with co-occurrence of substance use disorders. CCM will be associated with better outcomes for substance abusing SMI and will be the less costly treatment for them. There will be No difference in outcomes between CCM and EBT for subjeCts without co- occurring substance abuse, but EBT will be less costly. Results of this study should increase knowledge about the client groups who will most benefit from clinical case management, increase understanding of the specific advantages of clinical case management models, and contribute to development of improved Comprehensive services for the SMI with co- occurring substance use disorders.